April 24, 2013

New Nanofiber Technology Set To Strengthen Composite Goods

Materials engineers at the University of Nebraska-Lincoln have developed a structural nanofiber that is found to posses both strength and toughness; two qualities that are traditionally mutually exclusive. Findings from their work will be published this week in the April issue of the American Chemical Society's journal, ACS Nano.

The materials engineers group made the nanofiber using polyacrilonitrile nanofiber, a synthetic polymer related to acrylic. The group used a process called electrospinning, where high voltage is applied to a polymer solution until a small jet of liquid ejects. This results in a continuous length of nanofiber. The group was able to spin an exceptionally thin polyacrilonitrile nanofiber using this process.

"Our discovery adds a new material class to the very select current family of materials with demonstrated simultaneously high strength and toughness," Dzenis added.

Typically a structural material possesses strength or toughness, but not both. "Strength refers to a material's ability to carry a load. A material's toughness is the amount of energy needed to break it; so the more a material dents, or deforms in some way, the less likely it is to break," the report said.

A real world example was also offered. "A ceramic plate can carry dinner to the table, but shatters if dropped, because it lacks toughness. A rubber ball is easily squished out of shape, but doesn't break because it's tough, not strong. Typically, strength and toughness are mutually exclusive."

The nanofiber gained both strength and toughness by spinning a thinner strand. It is believed, by Dzenis, that toughness comes from the nanofiber's low crystallinity. "In other words, it has many areas that are structurally unorganized. These amorphous regions allow the molecular chains to slip around more, giving them ability to absorb energy," the report said.

This goes along with historical learning. Most advanced fibers have fewer amorphous regions and break easily.

The new nanofiber can be used in products made from composite materials, such as airplanes, bridges, body armor and bicycles, among other objects. The new material could offer improvements, or new behaviors, over what is available in composite materials today.

"If structural materials were tougher, one could make products more lightweight and still be very safe," Dzenis said.

Co-authors on the report are mechanical and materials engineering colleagues Dimitry Papkov, Yah Zou, Mohammad Nahid Andalib and Alexander Goponenko, from UNL's Department of Mechanical and Materials Engineering, and Stephen Z.D. Cheng of the University of Akron. The National Science Foundation, the Air Force Office of Scientific Research and a US Army Research Office Multidisciplinary University Research Initiative grant jointly funded the research.

More work has been done on nanofibers, including using different materials and processes to create materials for different uses.